Devices for detecting and generating a warning with respect to dangerous conditions, such as the presence of carbon monoxide (CO), are known. For example, various devices and systems are described in U.S. Pat. Nos. 5,517,182 to Yasunaga, issued on May, 14, 1996; 5,694,118 to Park et al., issued Dec. 2, 1997, 5,886,639 to Tanguay, issued Mar. 23, 1999, and 6,819,256 to Johnston et al., issued Nov. 16, 2004, the contents of all which are expressly incorporated by reference in their entirety.
In general, CO detectors employ one of three types of detectors: semiconductor, biomimetic and electrochemical.”
Semiconductor CO sensors typically employ a thin layer of metal, such as tin dioxide, maintained at a relatively high temperature (e.g., 100.degree. C. to 400.degree. C.). The surface conductivity of the metal varies generally proportionally in accordance with exposure to ambient CO concentration. The semiconductor chip measures the migration of oxygen molecules through the surface of the sensor material.
Biomimetic sensors utilize a transparent substrate disk coated with a synthetic hemoglobin that mimics the reaction of natural hemoglobin in the presence of carbon monoxide. The biomimetic material darkens with cumulative absorption of CO. A light emitting diode (LED) transmits light through the biomimetic material to a photosensitive device. When the material becomes sufficiently dark to prevent adequate light from reaching the photosensitive device, the detector sounds an alarm.
Electrochemical sensors, in general, employ a chemical reaction to convert CO to carbon dioxide (CO2) to create a chemical imbalance in a portion of the cell which in turn generates a current indicative of the amount of CO present. Some electrochemical sensors utilize two chambers (one for CO and one for hydrogen).